The present invention relates to the production of fatty acid methyl esters from mixtures of triglycerides and fatty acids. In particular, the invention relates to a single-phase process, which may be referred to as a two-step process, for production of fatty acid methyl esters from mixtures of triglycerides and fatty acids. The process does not require separation of any phases in intermediate steps in the process.
The transesterification of vegetable oils to form esters, and in particular, methyl esters, has received considerable attention, primarily because the esters may be used as xe2x80x9cbiofuelsxe2x80x9d or xe2x80x9cbiodieselxe2x80x9d. Biofuels are fuels derived from renewable resources such as naturally occurring fats and oils. Such fats and oils may be obtained from a variety of plant and animals. Biodiesel relates to the specific application to diesel fuel.
The major components of an oil or fat are fatty acid triglycerides, in which three long chain fatty acid moieties are joined to one glycerol moiety by ester linkages, particularly when the fats and oils are in the form of vegetable oils. Other sources of fats and oils contain a significant proportion of fatty acids. Such fatty acids may include lauric acid, palmitic acid, stearic acid, oleic acid and linoleic acid.
A number of manufacturing facilities have been built in Europe for the manufacture of biofuels, and similar facilities are planned for other countries.
The formation of vegetable oil methyl esters by the base-catalyzed reaction of triglycerides in the vegetable oil with methanol is a two-phase reaction, and is known to be slow. The problem of the slow reaction rate may be alleviated by the use of non-reactive co-solvents, which result in the conversion of the two-phase system into a single-phase system. Simple ethers, such as tetrahydrofuran (THF) and methyltertiarybutylether (MTBE), are particularly good co-solvents, as is described in Canadian Patent Application 2,131,654, published Mar. 9, 1996. Molar ratios of alcohol to triglyceride of at least 4.5:1 and more preferably at least about 6:1 are disclosed, with typical ratios being in the range of 6:1 to 8:1. The reaction is further discussed by D. G. B. Boocock et al in Biomass and Bioenergy Vol. 11, No. 1 pp 43-50 (1996).
Canadian Patent Application 2,131,654 states that free fatty acids are particularly troublesome components of fats and oils. In particular, when a transesterification of the oil (triglyceride) using a base catalyst is attempted in the presence of fatty acids, the free fatty acids form soaps on neutralization by the base catalyst.
U.S. Pat. No. 4,164,506 of Kawahara et al. discloses a process involving (a) esterification of free fatty acids in the presence of an acid catalyst, (b) allowing the product mixture to separate into a fat layer and an alcohol layer so as to obtain a refined fat layer, and (c) then subjecting the fat layer to transesterification with a base catalyst.
U.S. Pat. No. 4,695,411 of Stern et al. discloses a multi-step reaction involving acid transesterification with alcohol in the presence of 1-60% water and separating a glycerol phase that is obtained, reducing the free acidity of the remaining ester phase and then transesterification in the presence of a base catalyst.
U.S. Pat. No. 4,698,186 of Jeromin et al. discloses a process for reducing the free acid content of fats and oils by esterification with an alcohol in the presence of an acidic cation exchange resin.
U.S. Pat. No. 5,525,126 of Basu et al teaches esterification of mixtures of fats and oils by using a calcium acetate/barium acetate catalyst. However, the method requires elevated temperature (in excess of 200xc2x0 C.) and pressure (approximately 500 psi). The reaction time (three hours) is long. These conditions render the process impractical and uneconomical.
U.S. Pat. No. 5,713,965 of Foglia et al. teaches use of lipases to transesterify mixtures of triglycerides and free fatty acids. The reactions require 4-16 hours to reach conversion rates of 95%, which is not practical for an industrial process.
Improvements in processes for the production of fatty acid methyl esters from mixtures of fatty acids and triglycerides are required. In particular, a process for the conversion of fatty acids and triglycerides to the corresponding ester in a manner that is fast, essentially complete and is cost effective for both capital and operating costs is required. Such a process would offer potential as an industrial process.
Processes for the production of fatty acid methyl esters from mixtures of triglycerides and fatty acids have now been found.
Accordingly, one aspect of the present invention provides a single phase process for the esterification of a mixture of fatty acids and triglycerides, comprising:
(a) forming a solution of said fatty acid and triglycerides, an alcohol, an acid catalyst and a cosolvent at a temperature that is less than the boiling point of the solution, said alcohol being selected from the group consisting of methanol and ethanol, or mixtures thereof, and the ratio of said alcohol to said triglycerides and fatty acid being in the range of 15:1 to 35:1, the cosolvent being in an amount to effect formation of the single phase;
(b) maintaining the solution for a period of time to effect acid-catalyzed esterification of the fatty acids;
(c) neutralizing the acid catalyst and adding a base catalyst for the transesterification of said triglycerides; and
(d) after a further period of time, separating esters from said solution.
In preferred embodiments of the invention, the triglyceride is selected from the group consisting of beef tallow, coconut oil, corn oil, cottonseed oil, lard, olive oil, palm oil, palm kernel oil, peanut oil, soybean oil, linseed oil, tung oil, sunflower oil, safflower oil, canola oil, rapeseed oil, sesame oil, babassu oil, perilla oil, oiticica oil, fish oils, menhaden oil, castor oil, Chinese tallow tree oil, Physic nut oil, Cuphea seed oil, microalgal oils, bacterial oils and fungal oils.
In a further embodiment of the invention, the cosolvent is selected from the group consisting of tetrahydrofuran, 1,4-dioxane, diethyl ether, methyltertiarybutylether and diisopropyl ether.
In another embodiment of the invention, the process is a continuous process.